Brown algae contain many kinds of sulfated polysaccharides. For example, the following sulfated fucose-containing polysaccharides are known: (1) sulfated fucans which consist of fucose and sulfate groups; (2) sulfated fucoglucuronomannans which contain glucuronic acid, mannose, fucose and sulfate groups, e.g., the sulfated fucose-containing polysaccharide-U as described in WO 97/26896 (approximate molar ratio of constituting saccharides, fucose:mannose:galactose:uronic acid:sulfate group=10:7:4:5:20; hereinafter referred to as U-fucoidan); and (3) sulfated fucogalactans which consist of fucose and galactose, e.g., the sulfated fucogalactan as described in PCT/JP00/00965 (molar ratio of constituting saccharides, fucose:galactose=1:1–6; hereinafter referred to as G-fucoidan).
These polysaccharides are generically called fucoidans or fucoidins. In many cases, their structures vary depending on the algae from which they derive. For example, sulfated polysaccharides extracted from Fucus vesiculosus, Laminaria japonica Areschoug, Cladosiphon okamuranus Tokida, Nemacystus decipiens (Suringar) Kuckuck and sporophyll of Undaria pinnatifida (Harvey) Suringar are known to have structures different each other. Almost all of these sulfated fucose-containing polysaccharides are macromolecular anions. Therefore, they behave in a chemically and physically similar manner in various purification steps, making it difficult to separate them each other. For this reason, in many cases, biological activities of sulfated fucose-containing polysaccharides derived from brown algae have been examined without separating them each other. For example, a sulfated fucan fraction has been reported to have a strong anticoagulant activity, whereas a sulfated fucoglucuronomannan fraction has been reported to have an apoptosis-inducing activity against tumor cells. However, it was difficult to identify the sulfated fucose-containing polysaccharide that was responsible for the observed biological activity.
If a physiologically active sulfated polysaccharide is to be developed as a pharmaceutical, it is necessary to determine its chemical structure. For this purpose, an enzyme that degrades the physiologically active sulfated polysaccharide is required. Similarly, if oligosaccharides are to be obtained from the above-mentioned sulfated polysaccharides, it is required to obtain enzymes that degrade the respective sulfated polysaccharides.
However, no enzyme that degrades a sulfated polysaccharide from brown algae is commercially available. In addition, a degrading enzyme that specifically degrades the sulfated polysaccharide of which the structure is to be determined is required. This is because, in many cases, sulfated polysaccharides from brown algae vary depending on the species of the algae. For example, a microorganism that utilizes a certain sulfated polysaccharide is often screened in order to obtain an enzyme that degrades the sulfated polysaccharide. In this case, a sulfated polysaccharide-degrading enzyme may be efficiently produced by isolating and identifying a microorganism that utilizes the sulfated polysaccharide, and examining culture conditions. However, it takes a long time to isolate and identify such a microorganism. Furthermore, it is not usual that a single microorganism utilizes more than one sulfated polysaccharides. Almost no microorganism is known to utilize sulfated polysaccharides from brown algae belonging to several orders or families.
Thus, it has been desired to produce a sulfated polysaccharide-degrading enzyme using an already identified and isolated microorganism, or to produce a several kinds of sulfated polysaccharide-degrading enzymes from a single microbial strain.
Recently, the following studies were reported with respect to a sulfated polysaccharide from Cladosiphon okamuranus Tokida: the polysaccharide inhibits colonization of Helicobacter pyroli, a gastric ulcer-causing microorganism, on tunica mucosa ventriculi; a complex of the polysaccharide with fibroblast growth factor can be used as an agent for promoting growth of fibroblasts; and infection with a bacterium, a virus or the like can be prevented by oral administration of the polysaccharide. Accordingly, relationships between physiological activities connected with Cladosiphon okamuranus Tokida and chemical structures of sulfated polysaccharides derived from Cladosiphon okamuranus Tokida have been studied. For example, there are two reports on the polysaccharides. One describes a sulfated glucuronofucan containing fucose, glucuronic acid, sulfate group and acetyl group with a molar ratio of 6.1:1.0:2.9:1 and having a molecular weight of about 56,000 (Glycoconjugate Journal, 16:19–26 (1999)). The other describes a sulfated glucuronofucan containing fucose, glucuronic acid, xylose, sulfate group and acetyl group with a molar ratio of 3–4:0.8–1.2:0.1–0.3:0.8–1.2:0.5–1 and having a molecular weight of about 500,000–600,000 (Oyo Toshitsu Kagaku (Journal of Applied Glycoscience), 43:143–148 (1996)). To date, only average values for the structures have been shown based on physicochemical analyses.
In addition, it is necessary to obtain an oligosaccharide having a uniform structure in order to develop a pharmaceutical or the like. However, it has been difficult to obtain an oligosaccharide having a uniform structure, for example, from a sulfated polysaccharide derived from Cladosiphon okamuranus Tokida.
For the reasons as described above, a microorganism that degrades many kinds of sulfated polysaccharides derived from brown algae, an enzyme that specifically degrades a sulfated polysaccharide derived from Cladosiphon okamuranus Tokida (i.e., a sulfated glucuronofucan) and a sulfated glucuronofucan oligosaccharide having a uniform structure produced by an enzymatic means have been desired.